1. Field of the Invention
The present invention relates to a tape speed control apparatus used in a tape running system of a video tape recorder (VCR) or the like.
2. Description of the Prior Art
A tape running system of a magnetic recording and reproducing apparatus, such as a VCR, have a supply reel on which a tape is wound and a take-up reel for taking up the tape drawn from the supply reel. In general, the take-up reel is driven by a take-up reel motor so as to control a tape speed at which the tape is transferred and the supply reel is driven by a supply reel motor to keep the tension of the drawn-out tape at a specific tension.
Hitherto, it has been attempted to detect the speed of the tape or the rotatinal speed of the take-up reel and control the tape transfer by a feedback control system. For example, the tape speed is detected and compared with a tape speed command. If the detected tape speed is smaller than the tape speed command, the torque of a take-up reel motor for driving the take-up reel is increased to accelerate the take-up reel motor. If the detected tape speed is larger than the tape speed command, the torque of the take-up reel motor is decreased to decelerate the motor. As a result, the tape speed is controlled such that the detected tape speed and the command may coincide with each other.
In such a conventional constitution, a time delay occurs in the response of the tape speed to the tape speed command. Accordingly, there are serious problems in operability. For example, 1) the tape speed cannot respond to a quick change of the tape speed command set from outside, 2) the acceleration of the tape to the maximum speed takes a considerable amount of time, and 3) the tape fairly goes beyond a position at which an operator wishes to stop the tape during a high speed search. Since in particular, the VCRs for professional use are frequently used in editing, the improvement in the response of the tape speed to a shuttle dial operation has been demanded.
In addition, the overshoot of the tape speed sometimes occurs. In the case of changing from the state of a high speed search to the state of pause in a VCR, the tape stops through the temporary state of reverse playback once. This operation badly affects the feeling of the operability.